Multiple monoaminergic modulation of posturo-locomotor network activity in the newborn rat spinal cord.
Front. Neural Circuits.. 2014-08-15; 8:
DOI: 10.3389/fncir.2014.00099
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Studies devoted to understanding locomotor control have mainly addressed the
functioning of the neural circuits controlling leg movements and relatively
little is known of the operation of networks that activate trunk muscles in
coordination with limb movements. The aim of the present work was (1) to identify
the exogenous neurotransmitter cocktail that most strongly activates postural
thoracic circuitry; (2) to investigate how the biogenic amines serotonin (5-HT),
dopamine (DA), and noradrenaline (NA) modulate the coordination between limb and
axial motor networks. Experiments were carried out on in vitro isolated spinal
cord preparations from newborn rats. We recorded from ventral roots to monitor
hindlimb locomotor and axial postural network activity. Each combination of the
three amines with excitatory amino acids (EAAs) elicited coordinated rhythmic
motor activity at all segmental levels with specific characteristics. The
variability in cycle period was similar with 5-HT and DA while it was
significantly higher with NA. DA elicited motor bursts of smaller amplitude in
thoracic segments compared to 5-HT and NA, while both DA and NA elicited motor
bursts of higher amplitude than 5-HT in the lumbar and sacral segments. The
amines modulated the phase relationships of bursts in various segments with
respect to the reference lumbar segment. At the thoracic level there was a phase
lag between all recorded segments in the presence of 5-HT, while DA and NA
elicited synchronous bursting. At the sacral level, 5-HT and DA induced an
intersegmental phase shift while relationships became phase-locked with NA.
Various combinations of EAAs with two or even all three amines elicited rhythmic
motor output that was more variable than with one amine alone. Our results
provide new data on the coordinating processes between spinal cord networks,
demonstrating that each amine has a characteristic « signature » regarding its
specific effect on intersegmental phase relationships.